Long-term no tillage alleviates subsoil compaction and drought-induced mechanical impedance

. No tillage was introduced to Northeast China to prevent the soil degradation caused by conventional tillage systems. However, there are concerns that no tillage will result in soil mechanical impedance. In this study, we investigated the effects of conventional tillage and no tillage on soil strength properties using a long-term field study initiated in 2011 on a silt clay loam soil. In 2018 and 2019, soil bulk density, water content, the degree of compactness, and penetrometer resistance were measured before tillage and after planting, and also, the changes in soil profile water content and penetrometer resistance were monitored during drying periods. Results showed that conventional tillage led to the formation of a compacted zone beneath the cultivated layer, with higher bulk density, degree of compactness, and penetrometer resistance values. After converting from conventional tillage to no tillage for 8 to 9 years, the bulk density, penetrometer resistance, and degree of compactness were increased to a moderate extent in the topsoil but were lowered in the subsurface soil. During drying periods, as compared to conventional tillage plots, the no tillage plots maintained higher water contents, which resulted in lower penetrometer resistances below a 15 cm depth and the later arrival of the threshold penetrometer resistance of 2 MPa. Long-term no tillage alleviated subsoil compaction and retarded drought-induced soil strength development.